Abstract
The GammaTPC is an MeV-scale single-phase liquid argon time-projection-chamber gamma-ray telescope concept with a novel dual-scale pixel-based charge-readout system. It promises to enable a ...significant improvement in sensitivity to MeV-scale gamma rays over previous telescopes. The novel pixel-based charge readout allows for imaging of the tracks of electrons scattered by Compton interactions of incident gamma rays. The two primary contributors to the accuracy of a Compton telescope in reconstructing an incident gamma-ray’s original direction are its energy and position resolution. In this work, we focus on using deep learning to optimize the reconstruction of the initial position and direction of electrons scattered in Compton interactions, including using probabilistic models to estimate predictive uncertainty. We show that the deep-learning models are able to predict locations of Compton scatters of MeV-scale gamma rays from simulated 500
μ
m pixel-based data to better than 1 mm rms error and are sensitive to the initial direction of the scattered electron. We compare and contrast different deep-learning uncertainty estimation algorithms for reconstruction applications. Additionally, we show that event-by-event estimates of the uncertainty of the locations of the Compton scatters can be used to select those events that were reconstructed most accurately, leading to improvement in locating the origin of gamma-ray sources on the sky.
P-type point contact (PPC) HPGe detectors are a leading technology for rare event searches due to their excellent energy resolution, low thresholds, and multi-site event rejection capabilities. We ...have characterized a PPC detector’s response to
α
particles incident on the sensitive passivated and p
+
surfaces, a previously poorly-understood source of background. The detector studied is identical to those in the
Majorana
Demonstrator
experiment, a search for neutrinoless double-beta decay (
0
ν
β
β
) in
76
Ge.
α
decays on most of the passivated surface exhibit significant energy loss due to charge trapping, with waveforms exhibiting a delayed charge recovery (DCR) signature caused by the slow collection of a fraction of the trapped charge. The DCR is found to be complementary to existing methods of
α
identification, reliably identifying
α
background events on the passivated surface of the detector. We demonstrate effective rejection of all surface
α
events (to within statistical uncertainty) with a loss of only 0.2% of bulk events by combining the DCR discriminator with previously-used methods. The DCR discriminator has been used to reduce the background rate in the
0
ν
β
β
region of interest window by an order of magnitude in the
Majorana
Demonstrator
and will be used in the upcoming LEGEND-200 experiment.
Neutrinoless double-beta decay searches seek to determine the nature of neutrinos, the existence of a lepton violating process, and the effective Majorana neutrino mass. The Majorana Collaboration is ...assembling an array of high purity Ge detectors to search for neutrinoless double-beta decay in 76Ge. The Majorana Demonstrator is composed of 44.8 kg (29.7 kg enriched in 76Ge) of Ge detectors in total, split between two modules contained in a low background shield at the Sanford Underground Research Facility in Lead, South Dakota. The initial goals of the Demonstrator are to establish the required background and scalability of a Ge-based, next-generation, tonne-scale experiment. Following a commissioning run that began in 2015, the first detector module started physics data production in early 2016. We will discuss initial results of the Module 1 commissioning and first physics run, as well as the status and potential physics reach of the full Majorana Demonstrator experiment. The collaboration plans to complete the assembly of the second detector module by mid-2016 to begin full data production with the entire array.
Imperfections in analog-to-digital conversion (ADC) cannot be ignored when signal digitization requirements demand both wide dynamic range and high resolution, as is the case for the Majorana ...Demonstrator 76 Ge neutrinoless double-beta decay search. Enabling the experiment's high-resolution spectral analysis and efficient pulse shape discrimination required careful measurement and correction of ADC nonlinearities. A simple measurement protocol was developed that did not require sophisticated equipment or lengthy data-taking campaigns. A slope-dependent hysteresis was observed and characterized. A correction applied to digitized waveforms prior to signal processing reduced the differential and integral nonlinearities by an order of magnitude, eliminating these as dominant contributions to the systematic energy uncertainty at the double-beta decay <inline-formula> <tex-math notation="LaTeX">Q </tex-math></inline-formula> value.
The Majorana Collaboration has assembled an array of high purity Ge detectors to search for neutrinoless double-beta decay in 76Ge with the goal of establishing the required background and ...scalability of a Ge-based next-generation ton-scale experiment. The Majorana Demonstrator consists of 44 kg of high-purity Ge (HPGe) detectors (30 kg enriched in 76Ge) with a low-noise p-type point contact (PPC) geometry. The detectors are split between two modules which are contained in a single lead and high-purity copper shield at the Sanford Underground Research Facility in Lead, South Dakota. Following a commissioning run that started in June 2015, the full detector array has been acquiring data since August 2016. We will discuss the status of the Majorana Demonstrator and initial results from the first physics run; including current background estimates, exotic low-energy physics searches, projections on the physics reach of the Demonstrator, and implications for a ton-scale Ge-based neutrinoless double-beta decay search.
The MAJORANA DEMONSTRATOR is an experiment constructed to search for neutrinoless double-beta decays in germanium-76 and to demonstrate the feasibility to deploy a ton-scale experiment in a phased ...and modular fashion. It consists of two modular arrays of natural and 76Ge-enriched germanium p-type point contact detectors totaling 44.1 kg, located at the 4850' level of the Sanford Underground Research Facility in Lead, South Dakota, USA. The DEMONSTRATOR uses custom high voltage cables to bias the detectors, as well as custom signal cables and connectors to read out the charge deposited at each detectors point contact. These low-mass cables and connectors must meet stringent radiopurity requirements while being subjected to thermal and mechanical stress. A number of issues have been identified with the currently installed cables and connectors. An improved set of cables and connectors for the MAJORANA DEMONSTRATOR are being developed with the aim of increasing their overall reliability and connectivity. We will discuss some of the issues encountered with the current cables and connectors as well as our improved designs and their initial performance.
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